Has anyone got a working Bluetooth GPS receiver for the Archos tablet, if so what make is it and where can it be bought?
What is the turn-by-turn navigation like on the Archos tablets/Android, can it rival TomTom and the likes?

Hi. You can use an extern Bluetooth GPS like this one : Holux m-1000B for 31.79€. It works with the Archos gen 8 tablets. Then you only have to download an application like "Bluetooth GPS Mouse" which obviously works with the Archos android tablet. I forget to say, you need the hack of the market and android 2.2 (last firmware) to use it.
A rival of a TomTom? I don't think so but I don't, I haven't the two devices. Maybe u can see some screenshot of the apk on the internet.